There are many known types of welding systems used for many different welding processes. Welding system, or system for welding, as used herein, includes one or more of a power source, controller, wire feeder, and a source of gas, it may also include peripherals such as robots etc. Welding power supply, as used herein, includes any device capable of supplying welding, plasma cutting, and/or induction heating power including power circuitry, control circuitry and other ancillary circuitry associated therewith.
One type of welding system includes a current controlled welding power source. A current controlled welding power source, as used herein, is a current controlled power source, wherein the output current is monitored, and the output is adjusted to provide the desired current. The current may be constant during the welding process, or may have a desired waveform of varying current. Current controlled, as used herein, is an output controlled to provide a desired current output.
Another type of welding system includes a voltage controlled power source. A voltage controlled welding power source, as used herein, is a voltage controlled power source, wherein the output voltage is monitored, and the output is adjusted to provide the desired voltage. The voltage may be constant during the welding process, or may have a desired waveform of varying voltage. Some voltage controlled welding power sources use a current command, and adjust the current in response to the monitored voltage, thereby adjusting the arc voltage by the change in current across the load.
One known welding process is a pulsed MIG process. A pulsed MIG process typically has a cyclical output having at least a peak segment with a relatively high current and a background segment with a relatively low current. A typical prior art pulsed MIG waveform is shown in FIG. 1, and includes a flat peak 101, a background 102, and steep transitions 103 and 104 between them. There is often an abrupt change in slope from at the beginning and end of the peak and background portions. Pulse welding, as used herein, includes welding with output power that is generally pulsed, at a controllable frequency, between a greater peak and a lesser background.
Undesirable arc noise is generated by the sharp edges in the waveform. Also, the sharp slope changes can cause difficulty when welding with specialty wires such as Inconel®, Monel®, and Hastelloy®, as well as aluminum, metalcore and stainless wires. For example, using such wires with prior art pulsed MIG can result in sharp edges or craters at the edges of the weld where it meets the plate. Moreover, fast slope changes from peak to background can result in arc outages at lower currents. Fast slope changes from peak to background and back to peak can cause over and under shoots of the current.
Prior art U.S. Pat. Nos. 5,742,029 and 5,001,326 discussed controlling the amount of energy in a surface tension transfer process pulse by providing an exponential decay during the tail out. However, that process also taught very rapid transitions from peak to background in other portions of the pulse. Thus, it failed to satisfactorily address arc noise.
Other prior art systems such as the Miller Pulse Star® and Summit Arc® were phase controlled systems with sinusoidal outputs that might provide less abrupt transitions, but operate at either fixed frequencies or harmonic frequencies.
One prior art patent, U.S. Pat. No. 6,909,067, used a combination of a fast current controlled ramp followed by a slower voltage controlled ramp to soften corners. This was better than the prior art, but was operative only at the beginning and end of the peak and background portions, and not during the entire transition.
Accordingly, a control scheme for pulsed MIG that provides for gradual slope changes or non-zero acceleration from peak to background and background to peak is desirable.